Background: This study investigated the relationship between gratitude, purpose in life and flourishing, as well as the mediating role of purpose in life in the relationship between gratitude and flourishing in two different cultures, Indian and Polish. We also examined the moderating role of gender in the relationship between gratitude and purpose in life. Methods: A sample of 328 Indian and 303 Polish participants aged 18–56 years completed the Gratitude, Resentment, and Appreciation Scale, the Purpose in Life Questionnaire, and the Flourishing Scale. Pearson’s correlations were used to assess the associations between the main study variables, and PROCESS software was used to calculate moderated mediation. Results: Findings showed that gratitude and purpose in life were positively related to flourishing. Life purpose mediated the relationship between gratitude and flourishing. In the Indian sample, gender was a statistically significant moderator between gratitude (and its three facets) and purpose in life. In the Polish sample, gender moderated the relationship between overall gratitude and only one dimension (a sense of abundance) and purpose in life. Conclusions: The results suggest that enhancing gratitude and a sense of purpose in life can significantly improve individuals’ flourishing, considering gender and cultural differences.